Esther M. Sánchez-Carnerero

Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores

Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) O-BODIPYs (R)-1 and (S)-1 by irradiation with visible light is first detected as proof of the ability of a new structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|glum|) in solution falls into the usual range of that obtained from other simple organic molecules (10–5–10–2 range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1′-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications.

Bis(haloBODIPYs) with Labile Helicity: Valuable Simple Organic Molecules That Enable Circularly Polarized Luminescence

Simple organic molecules (SOM) based on bis(haloBODIPY) are shown to enable circularly polarized luminescence (CPL), giving rise to a new structural design for technologically valuable CPL-SOMs. The established design comprises together synthetic accessibility, labile helicity, possibility of reversing the handedness of the circularly polarized emission, and reactive functional groups, making it unique and attractive as advantageous platform for the development of smart CPL-SOMs.

Dual stereoselection in the addition of diethylzinc to benzaldehyde by using highly structurally close ligands

The screening of the catalytic activity in the diethylzinc reaction of a series of easily accessible (1S)-ketopinic-acid derived hydroxyamides, designed by key structure modifications of a parent highly active related bis(hydroxyamide), has allowed to find the first case of dual stereoselection in highly structurally close ligands of such interesting chemically sustainable typology. The found striking dual stereoselection is explained on the basis of empiric models for the acting zinc catalysts and involved controlling transition states, which are supported by additional specific experimental structure-activity tests.

Unexpected efficiency of non-C2-symmetric bis(hydroxyamide)-based zinc-chelate catalysts†

Asymmetric bis(hydroxyamide)-based zinc-chelate catalysts are able to promote the enantioselective addition of diethylzinc to benzaldehyde in the absence of titanium with yields and ees comparable, or inclusively superior, to their C(2) -symmetric analogues. This unexpected fact demonstrates that the previously established assumption on the necessity of using C(2) -symmetric bis(hydrdoxyamides) to generate C(2) -symmetric zinc-chelate catalysts can be discarded, which expand the possibilities for designing new ligands based on the interesting hydroxyl-amide functional grouping.

Cheap and long-life reusable polymer for asymmetric organozinc catalysis based on camphor-derived hydroxyamides.

Polystyrene grafted with a chiral zinc-complexing camphor-derived N,N-disubstituted hydroxyamide is proposed as a new type of functional polymer of high reusability for the development of sustainable organozinc-catalyzed asymmetric reactions. The main goal of this new functional polymer is the ease of the hydroxyamide-moiety preparation (cheap chiral ligand obtained straightforwardly from an enantiopure starting material coming from the chiral pool), as well as its chemical robustness when compared with other related zinc-complexing functional groups. The latter allows the polymer to be active after multiple applications, without significant loss of its catalytic activity. This fact is exemplified by the design and preparation of a polymer functionalized with a bis(hydroxyamide) proved previously as active in the homogeneous enantioselective addition of diethylzinc to aldehydes. The result is a cheap functional polymer with a very high reusability (the enantioselectivity and chemical yield are maintained practically constant after 20 applications). Additionally, a methodology for the multicycle use of these functional polymers is presented.

Chiroptical behavior of BINOL-based spiranic O -BODIPYs. A study on the influence of the structural factors

Spiranic O-BODIPYs bearing a phenol-based bi(polyarene) unit tethered to the boron center through oxygen atoms constitute an interesting family of BINOL-BODIPY dyads useful for the development of photonic applications due to their synthetic accessibility and tunable photonic properties. We found previously that the electron-donor capability of the involved BINOL moiety switched on a non-emissive intramolecular charge transfer (ICT) state, which restricted the fluorescence efficiency of the dyad. We demonstrated that the influence of this non-radiative deactivation channel can be efficiently modulated by the substitution pattern, either at the dipyrrin core or at the polyarene moiety, being possible to diminish or even virtually cancel the ICT probability, and hence achieve bright fluorescence upon dual excitation at far-away spectral regions.1 Additionally, we demonstrated that this simple structural motif exhibits chiroptical properties (circular dichroism, CD, and circularly polarized luminescence, CPL), as a consequence of the chiral perturbation exerted by the BINOL-based unit over the inherently achiral BODIPY chromophore.2 Based on these previous results, we found interesting to carry out a comprehensive study on the influence of the structure of both the BODIPY chromophore and the BINOL moiety over the chiroptical properties of this family of O-BODIPYs, directed to the improvement of said properties for their use in photonic applications. This communication reports the most important preliminary results obtained from this study, directed to the design of improved BODIPYs for Chiroptics. [1] Gartzia-Rivero, L.; Sanchez-Carnerero, E. M.; Jimenez, J.; Banuelos, J.; Moreno, F.; Maroto, B. L.; Lopez-Arbeloa, I.; de la Moya, S. Modulation of ICT probability in bi(polyarene)-based O-BODIPYs: towards the development of low-cost bright arene-BODIPY dyads. Dalton Trans. 2017, 46, 11830. [2] Sanchez-Carnerero, E. M.; Moreno, F.; Maroto, B. L.; Agarrabeitia, A. R.; Ortiz, M. J.; Vo, B. G.; Muller, G.; de la Moya, S. Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores. J. Am. Chem. Soc. 2014, 136, 3346.